For front-end sections of traditional radio transceivers, many external parts, such as baluns, semiconductor switches, and matching circuits, have been used. Many of these external parts, however, are being replaced by on-chip parts to reduce cost, save space, and so on.
For example, US Patent Application Publication No. 2013/0078931 (PTD 1) discloses a transmitting-receiving front end having a balun and a semiconductor switch that are integrated on-chip. As described in FIG. 2 of PTD 1, the transmitting-receiving front end includes a low-noise amplifier (LNA), a power amplifier (PA), a transformer (balun), a semiconductor switch, a matching circuit, and an antenna. Among these, the matching circuit and the antenna are external parts, and the others are on-chip parts.
Specifically, a differential signal output from the power amplifier is converted into a single-ended signal by the transformer. An output signal of the transformer is supplied to the antenna through the matching circuit. A signal received by the antenna, on the other hand, is input to the low-noise amplifier through the matching circuit and the semiconductor switch. The semiconductor switch is switched off at a time of a transmission operation, and is switched on at a time of a reception operation.